The body has different types of fat. White fat stores extra energy. Too much white fat builds up in obesity. Brown fat, in contrast, burns calories to create heat and help maintain body temperature. Researchers have been trying to harness brown fat’s activity in order to treat obesity, diabetes, and other metabolic disorders.

Certain compounds have “browning” effects on white fat. They increase metabolism and turn white fat cells into beige fat cells, which have some of the calorie-burning characteristics of brown fat. However, these drugs may have unwanted side effects in other parts of the body. Being able to deliver drugs directly to white fat may prevent or reduce side effects. Previous research showed that nanoparticles could deliver browning drugs to convert white fat cells into beige fat cells. Nanoparticles are microscopic particles that can be used to carry drugs and other substances in the body.

A team of researchers led by Drs. Li Qiang of Columbia University and Zhen Gu of the University of North Carolina at Chapel Hill and North Carolina State University set out to design a microneedle skin patch that could switch on fat browning in a targeted region. The study was supported by NIH’s National Center for Advancing Translational Sciences (NCATS) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Results were published on September 26, 2017, in ACS Nano.

The research team designed a skin patch with 121 cone-shaped polymer needles that can be filled with a drug encapsulated by nanoparticles. The tiny needles penetrate the skin and the ends collapse. The nanoparticles then slowly release the browning drug into the fat cells. By delivering the drug directly to fat cells, the drug’s side effects in other parts of the body might be prevented or minimized.

The researchers tested the skin patch, which was a little larger than a pencil eraser, on the abdominal fat pads of three groups of normal mice. The first group received a skin patch without any drug; the second group received a patch containing rosiglitazone (a diabetes drug that’s also known as Rosi or by its trade name Avandia); and the third group received a patch containing a compound called CL 316243. In mice treated with either drug, the white fat cells shrunk and beige fat cells appeared. A genetic analysis and other tests confirmed that both drugs induced fat browning and improved metabolism in the mice.

The research team then treated obese mice with skin patches for 4 weeks. The drugs increased browning, as evidenced by smaller fat cells and increased expression of brown fat cell genes. They also reduced the size of the fat pad and improved metabolic signs.

“There are several clinically available drugs that promote browning, but all must be given as pills or injections,” Qiang says. “This exposes the whole body to the drugs, which can lead to side effects such as stomach upset, weight gain, and bone fractures. Our skin patch appears to alleviate these complications by delivering most drugs directly to fat tissue.” The microneedle skin patch seems promising, but has not been tested in people.